Restraints and Freedom

I have been pondering the line between artificially, though self-imposed rules, and complete musical freedom in composing. One of my projects has been to create a melody or more using two motifs. I can use inversions, retrograde, transpositions of the motifs, but just those two chunks of intervals. Although I can intellectually come up with those melodies, they aren't very satisfying for me, in the end. I can start with the motif, but pretty soon, I want to add another note, or change direction slightly as I hear it in my mind.

Another project is to create melodies from different pentatonic scales. That gives me a little more freedom and is easier. The rules of the pentatonic counterpoint, though, are giving me a little trouble.

The tough project, right now, is to sketch out a 5 movement string quartet. I know that I can put some kinds of restraints on myself - perhaps the style of each movement, the basic tonality, the length of each movement. I do know, too, that once I start on a movement, it may take me in different directions than I had planned.